There is a general demand in the market for biodegradable surfactants that are produced from renewable raw materials as a suitable alternative to the currently available surfactants which are obtained from petrochemical raw materials. This demand is in particular accentuated with the foreseeable shortage of petrochemical raw materials and increasing demand for surfactants. Rhamnolipids are at least one example of such a surfactant. Rhamnolipids represent an economically interesting class because they may potentially replace conventional surfactants made from petroleum or products thereof, and thus invariably improve the environmental performance of the resulting formulations.
These rhamnolipids comprise at least one monorhamnosyl lipid or two rhamnose radicals (dirhamnosyl lipids) and one or two 3-hydroxy fatty acid residues (Handbook of Hydrocarbon and Lipid Microbiology, 2010). They have surface-active properties, which are needed in all sorts of applications for use as a surfactant (see Leitermann et al., 2009). In particular, rhamnolipids, may be employed to a large extent as surfactants in household, cleaning, cosmetic, food processing, pharmaceutical, plant protection and other applications.
The currently used methods to produce these rhamnolipids employ wild-type isolates of various human and animal pathogenic bacteria, particularly members of the genera Pseudomonas and Burkholderia, (Handbook of Hydrocarbon and Lipid Microbiology, 2010). The fact that these pathogenic organisms are capable of causing diseases to the consumer considerably reduces the customer's acceptance for these conventionally produced rhamnolipids. Further, higher safety requirements also increase the production costs owing to increased capital expenditure and possibly additional production steps. Since the products in which these rhamnolipds are used are mostly high volume chemicals which can be produced at very low costs, the rhamnolipids must also be able to be produced at costs as low as possible, without health risks for the customer and with defined properties as far as possible.
The current methods available for production of rhamnolipids include the use of these pathogenic organisms and vegetable oils as the sole or co-substrate (Handbook of Hydrocarbon and Lipid Microbiology, 2010). Vegetable oils, however, are comparatively expensive raw materials in comparison to other carbon sources, such as, for example, glucose, sucrose or polysaccharides such as, for example, starch, cellulose and hemicellulose, glycerol, CO, CO2 or CH4. Rhamnolipids are also produced by non-pathogenic organisms using carbon sources, such as, for example, glucose, sucrose or polysaccharides as taught in WO2012013554A1.
However, there still lies a need to produce rhamnolipids (in particular, monorhamnosyl lipid and/or dirhamnosyl lipids) efficiently (i.e. inexpensively and, from the health point of view, safely) and in more than adequate amounts using non-pathogenic organisms and an alternative renewable raw material.